The present invention relates to a system and method for measuring torque on a rotating shaft and particularly to a system and method for measuring torque on a rotating load coupling shaft for driving a power generator.
Various machines, such as a gas turbine and/or a steam turbine, may be used to drive a load such as a power generator. In particular, a gas turbine and/or a steam turbine may be used to rotate a magnet within a stator to generate electric power. The power generator includes a shaft which is connected to the rotating magnet and which itself is connected to a large connecting shaft (also called a load coupling shaft) rotated by one or more turbines. The connecting shaft is typically large and stiff, thereby resulting in very small torsional displacements (strains) when a torque is imposed on the connecting shaft. A measurement of torque transmitted through the connecting shaft is often made to determine the power output of the machine(s) rotating the connecting shaft.
The torque imposed on the connecting shaft has been measured in the past using strain gauges. However, the accuracy of torque measurements provided by strain gauges often does not meet engineering requirements because the uncertainty of such measurements is rather large as compared to the strains measured.
Accordingly, there remains a need in the art to measure torque on a rotating shaft, such as a rotating load coupling shaft for driving a power generator, with a high degree of accuracy. The present invention satisfies this need. For example, the present invention is capable of measuring torque of a rotating shaft within a +/xe2x88x920.5% accuracy.
A known digital light probe system, developed by GE Aircraft Engines, has been used for several applications in the past including measuring compressor rotating blade vibratory displacements.
In one exemplary embodiment of the invention, an apparatus and method comprises a rotatable shaft, at least one first target coupled on the rotatable shaft so as to rotate therewith, at least one second target coupled on the rotatable shaft so as to rotate therewith, a first probe for transmitting a first transmission signal to the first target and receiving a first response signal from the first target, a second probe for transmitting a second transmission signal to the second target and receiving a second response signal from the second target; and a processor operatively coupled to the first and second probes for determining a torsional displacement of the shaft based on at least the first and second response signals received by the first and second probes, respectively.
The processor may determine a torque imposed on the rotatable shaft based upon its torsional displacement. The processor may determine the torsional displacement based on the difference in time between when the first response signal is received by the first probe and when the second response signal is received by the second probe.
A magnet of a power generator may be coupled to the rotatable shaft to rotate therewith. At least one of a gas turbine and a steam turbine may rotate the rotatable shaft.
The first and second probes may be formed by laser probes and the first and second targets may include a reflective material so that the first transmission signal is a laser light signal and the first response signal is a laser light signal formed from a reflection of the first transmission signal by the first target and the second transmission signal is a laser light signal and the second response signal is a laser light signal formed from a reflection of the second transmission signal by the second target. The first and second targets may be coupled to the rotatable shaft on opposite axial ends thereof.
Another first target may be coupled on the rotatable shaft so as to rotate therewith. The first probe transmits the first transmission signal to the another first target and receives another first signal from the another first target, and the processor determines a vibration displacement of the rotatable shaft based on the first signal and the another first signal received by the first probe. The torsional displacement of the shaft may be determined based (at least in part) on the vibration displacement of the shaft.